The invention relates to a rotary actuator device for controlling the stroke of a charge exchange poppet valve in the cylinder head of an internal combustion engine.
To reduce the fuel consumption of internal combustion engines and to reduce pollutants in the exhaust gas, and furthermore to influence the torque performance of an internal combustion engine over the entire rotary speed range, valve operators have become known in which the open and close times of the intake and exhaust valves, as well as variable valve strokes in the intake valves are operated by means of electrical actuators controlled by electronic maps.
FR 2 608 675 A1 shows and describes a reciprocating internal combustion engine with a valve operator comprising several control cams for similar poppet valves of one cylinder. The cams are powered by an electronically mapped electric motor for the purpose of varying the open and close timing of the poppet valves relative to the crankshaft through a reference cylinder. Since in this known valve control with the various cams, the force of the closing spring has to be overcome when the poppet valve opens, a considerable amount of current is required for the electric motor and the rotary actuator. This places a considerable load on the on-board electrical system of a vehicle equipped with such an internal combustion engine.
It is known that this considerable current load on the electrical system or on-board network can be considerably reduced if an opening spring is associated with the closing spring of a poppet valve. Between the oppositely acting springs in the lifting of a gas exchange valve, the spring energies vary to reinforce the electromagnetic forces in the particular lift actuator, like the one disclosed for example by German Patent DE 30 24 109 C2. Such stroke actuators, which are configured as a mass-spring oscillating system for controlling the movement of a gas exchange valve, have especially the disadvantage of considerable structural height.
Lastly, U.S. Pat. No. 5,873,335 discloses a rotary actor device, in which a cam of common design driven by an electric motor cooperates with the poppet valve biased by a closing spring, and is in communication with a tappet, which is orthogonally disposed to the poppet valve and slides on the cam under the action of an opening spring. In this valve drive the oscillation of spring energies serves also to reduce the electrical energy drawn by the rotary actor. However, the disadvantage is especially in the unstable position of the control cam when the poppet valve is closed because the tappet is situated in the dome area under the biased opening spring. In the event of a slight deviation of the cam apex on the control cam, the spring produces a torque in the direction of rotation or contrary thereto and has to be compensated by a counter-torque of the actuated electrical rotary actor. This leads to a lengthy drain on the on-board electrical system, especially when the internal combustion engine is not running.
The invention addresses the problem of improving a rotary actor device for controlling the stroke of a poppet valve in the cylinder head of an internal combustion engine such that a control disk with a cam profile is perfectly secured in the end positions of the poppet valve when the internal combustion engine is not running, without powering the electric motor. Only relatively little to no electrical energy need be supplied to the electrical rotary actor to leave the secured positions.
One of the advantages of the invention is that, when the control disk is in its end position, overshooting is securely prevented. Further, due to the mechanical end stops, there is no need to supply current to the torsional pendulum motor to reach or retain an end position of the control disk. In the operation of the rotary actor device, the rotor in the rotary rocking motor is set in rotation up to a predetermined frequency of oscillation by a slight supply of energy to overcome the initial starting position. From then on the accumulated tension of the opening spring is converted to kinetic rotational energy of the rotor. The rotor is accelerated from the basic rotational phase until it reaches the cam ramp at the start of the cam flank. When the cam flank is reached the energy of the opening spring is substantially converted, while the control disk in co-rotation with the rotor has reached a maximum rotating speed. The charge change poppet valve is opened, the energy necessary for that purpose is taken from the kinetic rotational energy of the rotor, and the rotor speed begins to decrease. When the charge change poppet valve reaches its maximum opening stroke, the rotor's speed is virtually nil and the control disk affixed to the rotor reaches the second end abutment. The opening spring can in this case still exert a positive torque for securing the second rotary position or second starting position. This has the advantage that the valve-open position can be held according to the motor's requirements.
To close the charge change poppet valve, oppositely directed energy is fed to the rocker motor to leave the second starting position. Thereafter the rotor of the rocker motor is accelerated by the cam flank by the expanding closing spring of the poppet valve, and at the same time the tensing of the opening spring begins. During the closing action of the charge exchange valve, the rotor reaches a maximum velocity and kinetic energy, by which the opening spring is tensed through the lever attached to the shaft of the rotor, while the control disk already cooperates with the transfer element of the valve drive through the ground circuit. The rotation of the rotor is stopped against the first end rotation abutment up to a predetermined rocking frequency, and the starting position thus reached is secured according to the invention by the opening spring acting on the lever.
When the rotary actor device according to the invention is operated beyond the preset rocking frequency of the shaft, the starting position secured in each case is overcome by a ricochet movement produced by a resilient deformation of one of the colliding stops, which accelerates the shaft with the rotor in the direction of the ricochet movement such that the rocker motor does not have to be supplied with any substantial energy to make it leave the secured starting position.
An additional advantage of the invention is that during a prescribed cycle comprised of the opening and closing of a charge exchange valve, the necessary energy required by friction in the system and gas work at the charge exchange valve can be supplied at any time.
In a preferred embodiment of the invention, the control disk has a half cam profile which has a cam flank between a break-over point and a base circle for opening and closing. The cam flank has a ramp at which the control disk has in a diametric area a base circle section prolonged in the circumferential direction, which is adjoined by an abutment pointing substantially radially to the cam break-over area for the first end rotary abutment arranged on the motor or cylinder head side.
With the configuration described above, a control disk of reduced mass is advantageously achieved with an integrated abutment. Furthermore, with this control disk with a ramp provided between the base circle and the cam flank, the valve acceleration can be advantageously influenced to obtain good sound through additional control of the rocker motor.
In further development of the invention, the lever joined for rotation with the shaft adjacent the control disk bears in its free end area a ball-bearing mounted roller with a circumferential guiding groove, by which the free, biased spring arm wound in a screw thread manner and made of round wire is carried positioned in/on the cylinder head is borne as an opening spring over the turning range of the lever. The control disk in contact with the first end abutment when the poppet valve is closed is secured in this starting position by a bent end section of the spring arm which is urged against the roller.
With the use of a one-armed spring as the opening spring according to the invention, it is advantageously possible to achieve a compact spring of appropriate spring force requiring little space and ease of arrangement. Since it serves in an additionally advantageous manner also to secure abutment, the result according to a further proposal is that the end section is bent with respect to the spring arm such that a small component of force acting on the roller in the opening direction of the poppet valve is involved. Thus the starting energy input for the rocker motor is advantageously reduced.
This applies to the second rotary abutment according to an additional proposal, according to which the end section is further bent away from the arm of the spring such that, in the case of the maximum opening stroke of the poppet valve achieved at the second end rotary abutment, a torque approaching zero is produced.
The measures described above apply to the rotary actor device until a predetermined rocking frequency is reached by the shaft attached to the rotor.
In an additional embodiment of the invention, the first end rotary abutment when the internal combustion engine is not running can serve as a rest abutment, while for the increase of the dynamics with the internal combustion engine running in the area of the first starting position of the control disk, a dynamic initial positioning is performed by an electrical rocking stepper motor provided by a rotary actor, with the roller struck against the end section of the spring. A delivery of electric power to the rocker motor can in this case be so arranged that a stable position held slightly away from the action of the end section of the spring arm is achieved, which is quickly overcome in case of a signal for opening the charge exchange valve, which applies up to a predetermined rocker motor frequency.
Furthermore, a structurally advantageous embodiment of the second rotary stop is achieved by the invention by the fact that the end section of the spring arm of the coil spring bears a resilient abutment hook at its free end as the second end rotary abutment which limits the opening stroke of the poppet valve in cooperation with the roller, while the control disk has in the corresponding cam breakover point an arch coaxial with the shaft. With this arch uniform starting conditions are advantageously assured.
The invention makes possible, in addition to valve operation with maximum valve-open and valve-closed position, also a valve drive with variable strokes, for which it is further proposed that the rocking stepper motor performing alternating rotary movements by a control can be operated to achieve a variable stroke of the poppet valve at least in the opening direction in a microstepping operation. For this purpose the rotor can be stopped after a positive current by a negative current, and during the partial stroke it can be held by the corresponding rotor torque.
In order in this case to keep the need for energy relatively low, it is provided according to the invention that, for partial strokes of the poppet valve dependent on working point, the bias force of the spring arm acting on the lever is variable by changing the position of the spring arm relative to the cylinder head.
For low-friction valve operation it is furthermore proposed that the control disk cooperates with a roller type cam follower and that the roller type cam follower is arranged to be supported against the cylinder head through a valve play equalizing element. In further development, a rocking stepper motor can serve as rotary actor for a plurality of similar poppet valves of a cylinder of the internal combustion engine. Lastly, in addition to a roller type cam follower as an additional transfer means and, if desired, in combination with a hydraulic valve play equalizing element, a toggle lever and/or tappet are possible.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.